The fermentative production of the water-soluble polysaccharide xanthan gum by the action of Xanthomonas bacteria is well known. Xanthomonas hydrophilic colloid (“xanthan”) is an exocellular heteropolysaccharide. The heteropolysaccharide has a backbone chain of (1→4)β-glucose residues substituted by short, lateral chains linked to alternate monomeric residues of the main chain. Xanthan has a wide variety of industrial applications including use as a thickener, a stabilizing agent and a suspending agent, especially in foods. Furthermore, xanthan is used in oil well drilling muds and as a viscosity control additive in secondary recovery of petroleum by water flooding. Xanthan can also be used in cosmetic preparations, pharmaceutical delivery systems and similar compositions.
Xanthan is produced on an industrial scale by aerobic submerged fermentation of a bacterium of the genus Xanthomonas. The fermentation medium contains carbohydrate (such as sugar), trace elements and other nutrients. Once fermentation is complete, the resulting fermentation broth is heat-treated. Following heat-treatment, the xanthan is recovered by alcohol precipitation.
A well-recognised difficulty with xanthan gum has been its resistance to dispersibility and hydration. Typically, xanthan gum powder must be subjected to high agitation to get it to disperse and hydrate. Once dispersal and wetting are accomplished the hydration of the gum, as evidenced by the development of viscosity, is quite rapid.
In order to make xanthan gum more readily water-dispersible, several solutions have been proposed in the prior art.
U.S. Pat. No. 4,357,260 describes a dispersible xanthan gum composite consisting essentially of xanthan gum and silica wherein the ratio of xanthan gum to silica ranges from about 19:1 to 1:1.
U.S. Pat. No. 4,363,669 describes a dispersible, dry blend of glyoxal-treated xanthan gum and a non-dispersible plant gum selected from the group consisting of guar gum, tara gum, cold-water soluble tamarind gum, and cold-water soluble locust bean gum.
U.S. Pat. No. 4,654,086 is concerned with a dispersible blend consisting essentially of xanthan gum and a surfactant, which is one or more of lecithin, polyglycerol ester, propylene glycol ester, polyoxyethylene sorbitan ester, sorbitan ester, sodium stearoyl-2actylate, stearyl-2-lactylic acid, or polyoxylstearate, wherein the weight ratios of xanthan gum:surfactant range from 95:5 to 80:20.
U.S. Pat. No. 5,003,060 describes solid porous xanthan granules that are readily dispersible and soluble in water, said granules comprising at least one wetting agent, dispersing agent or a combination thereof.
Industrial applications of xanthan gum are primarily based on the polysaccharide's viscosity enhancing properties. Although xanthan gum is capable of producing highly viscous aqueous systems at relatively low concentrations, it would be highly advantageous to reduce the so called cost-in-use of xanthan gum by further improving the viscosity enhancing properties of xanthan gum.
U.S. Pat. No. 6,391,596 describes a high viscosity xanthan gum. This xanthan gum is characterised in that it has a sea water viscosity greater than 25 dial reading when dissolved in sea water to 0.29 weight percent.
U.S. Pat. No. 5,416,206 relates to a saline soluble xanthan gum having a viscosity of not less than 800 cP as determined on a 0.5% by weight solution thereof in a 12% by weight aqueous sodium chloride solution at 20° C. at 30 rpm using a Brookfield BL viscometer and having a ratio of this viscosity to that determined on a 0.5% by weight solution thereof in distilled water of not less than 1.5.
Kuhn et al. (Starch/Stäarke 41(12), 1989, 467-471) describe the results of experiments involving cooking extrusion of starch with hydrocolloids, including xanthan gum. The authors observe that cooking extrusion of starch with 5-30% xanthan gave products of high viscosity. The results presented in the article suggest that a co-extrudated blend of 5% xanthan and 95% corn starch exhibits a significantly higher viscosity than a dry mixed blend of 95% extruded corn starch and 5% xanthan.
Miladinov et al. (Industrial Corps and Products, 5 (1996), 183-188) describe experiments in which the viscous properties of starch and xanthan gum co-extruded with injection of adipoyl chloride were determined. Viscosities of aqueous solutions of ground extruded and non-extruded samples were compared. Extruded samples were found to have higher viscosities in distilled water solutions than the nonextruded materials.